1. Field of the Invention
The present invention relates to a sheet bundle treatment apparatus configured to perform center folding on a plurality of sheets.
2. Description of the Related Art
A sheet bundle treatment apparatus configured to bind a booklet by performing a saddle-stitch binding process and a center folding process on sheet bundles having a plurality of sheets on which images are formed by an image forming device is widely provided. When the center folding process is performed on a sheet bundle by the sheet bundle treatment apparatus as described above, a folded portion of the sheet bundle may be bulged and hence foldability may become insufficient. In particular, when the thickness of each sheet becomes large, the desired folded portion might not be formed, which may results in a low appearance quality of bound booklets.
Therefore, in U.S. Pat. No. 7,607,650, a pressing process to fortify a crease of the folded portion by press rollers which move along the folded portion of the sheet bundle while nipping the portion from both front and rear surfaces is performed after the center folding process. In U.S. Pat. No. 7,607,650, a flattening process is also performed to flatten a bulged part of a folded portion, or spine, of the sheet bundle by moving a flattening roller along the bulged part of the sheet bundle while pressing the portion. By selectively performing these processes, the appearance quality of the created bound booklet is improved.
In U.S. Pat. No. 7,607,650, when the flattening process or the pressing process is performed, an accuracy of positioning of the sheet bundle is enhanced by causing the sheet bundle being conveyed to abut against a retractable stopper. However, a motor or the like to move the stopper is additionally required, which leads to cost increase.
In order to achieve a stop position, to which the sheet bundle is conveyed, with high degree of accuracy without using the stopper, a timing to stop the motor that conveys the sheet bundle may be controlled with high degree of accuracy. In order to enhance the accuracy of the stop position of the sheet bundle, the velocity of conveyance of the sheet bundle to the position may be lowered. However, lowering of productivity is also resulted correspondingly.